1. Field of the Invention
This invention relates to implantable artificial devices for application in the human body. More particularly it is directed to a prosthetic device which substitutes for articulating anatomical joints.
2. Description of the Prior Art
The utilization of artificial devices which are implantable in the human body for replacing defective, damaged or diseased anatomical structure has long been known. One known specific form of prior art prosthetic device is for use in replacing anatomical joints of the body having ball and socket characteristics, as, for example, the hip joint. Such type of prosthesis essentially provides a detachable interconnection between the femur and acetabulum socket of the pelvis which serves the purpose of accomplishing the universal type movement associated with the replaced natural biological joint. Conventional prosthetic total hip joints normally embody an acetabulum type cup member having a spherical cavity which may be suitably secured in a variety of ways to the acetabulum socket of the pelvis, and an artificial femoral insert which is appropriately attached to the femur. The femur insert includes a smooth and substantially spherical head member which mates with and is rotatably supported by the spherical cavity of the cup member. As a result of this structural interrelationship a ball and socket type joint is created which permits the ordinary type of articulated motion associated with the human hip joint.
In this particular field there are several known approaches which provide for artificial articulated joints. By way of specific examples, reference is made to U.S. Pat. Nos. 3,813,699 and 3,863,273 primarily directed to implantable hip joint prostheses. The artificial hip joint generally described in the latter patent has a complicated construction. More specifically it requires the use of head and bearing insert members having rather precisely formed slots, grooves and projections which serve to cooperate with each other to form an assembled joint. Furthermore, the metallic outer shell of these devices is a necessary part of the assembly since one of its functions is to prevent the escape of the ball from the socket through deformation of the bearing insert. It will be appreciated that relatively significant manufacturing and cost factors tend to make the foregoing construction undesirable. The prostheses of both cited patents lack any provision whereby the artificial spherical femur head member is more tightly entrapped in the spherical cavity of the insert cup whenever the prosthesis is subject to forces which have a tendency to separate the femur head and the insert cup. Consequently, such types of prostheses are subject to joint dislocation. Additionally, neither of the described hip joint prostheses provides means which enable the insertion force associated with injecting the artificial femur head into the spherical cavity to be of a lesser magnitude than the force necessary to withdraw the femur head from the cavity.
Heretofore known prosthetic hip joint devices are characterized by relatively complicated structural arrangements which not only fail to effectively provide for a quick and easy insertion of the artificial femur head in the corresponding cavity of a cup member, but also fail to provide means which even more tightly entraps the femur head within the cavity in response to separation forces which would tend to dislocate or separate the femur head from the cavity.